The research objectives, of the Principal Investigator's work are: 1) To define the role of the oncogenic DNA simian virus 40 (SV40), in the in vivo experimental induction of neoplasis and in the in vitro neoplastic transformation of mammalian cells. It is of paramount importance to elicit whether such role is primary and essential, or secondary, similar to that of the co-carcinogenic factors; or whether it represents one of those non-specific stimuli which can promote but can not initiate carcinogenesis. 2) To determine the significance of alterations in the morphological and antigenic properties of SV40- transformed mammalian cells, in relation to the initiation and expression of the oncogenic state. It is of great interest to determine whether acquisition of neoplastic properties represents a gradual gain of new characters, some of which may be causally related to other manifestations of transformation, or if it represents the expression of inherent preexisting tendencies that may be indirectly promoted by the viral genome. 3) To determine the importance of the persistence of the SV40 viral genome within the genetic apparatus of the transformed mammalian cells, in relation to the maintenance, severity and progression of the oncogenic state.